This invention relates, in general, to a method and apparatus for measuring physical properties of golf club shafts and, more particularly, to a method and apparatus for measuring a vibrational characteristic or property of a golf club shaft.
In the field of designing, modifying, and fitting golf clubs, it is advantageous to know the physical properties of the golf club shaft as well as the physical properties of the golf club head. It is common in the industry to rate clubs based on the flexural stiffness designated typically by the terms: Extra Stiff (XS); Stiff (S); Firm (F); Regular (R); Average (A); and Ladies (L). The flexural stiffness is important because it determines the maximum bending as well as the first bending mode frequency of the shaft and, therefore by selecting the appropriate shaft stiffness, the club can be optimized for the swing speed of the particular golfer. The torsional stiffness of the golf club is also important because it determines the maximum windup of the club head relative to the shaft and the torsional frequency at which the club head oscillates about the axis of the golf club shaft during the swing. For optimum performance, in addition to matching the flexural stiffness of the shaft to the player""s swing speed, the torsional stiffness of the shaft should also be matched to the club head swing weight and the player""s swing speed. Another important physical property of the golf club shaft is its frequency of oscillation because it provides a reproducible and reliable index of shaft flexibility. Further, the frequency of oscillation allows frequency matching of golf clubs to form a set of golf clubs which have a substantially uniform xe2x80x9cfeelxe2x80x9d to the golfer.
A common prior art method for measuring the frequency of oscillation of the golf club shaft includes fixing one end of the shaft in a clamp and causing the club to vibrate or oscillate along a single axis. The vibrations are measured using several sets of light emitting diodes in combination with a counter. Limitations of this technique include the inability to measure oscillations along more than a single axis and the inability of the frequency measurement tools to properly operate when the golf club shaft oscillates in more than one axis.
The present invention provides a method and an apparatus for determining the frequency of oscillation or the vibrational frequency of a shaft by measuring the oscillatory behavior of the shaft. In a preferred embodiment of an apparatus for measuring the vibration of a golf club shaft incorporating features of the present invention, a clamping mechanism is provided for securing one end of a shaft to a support structure of the apparatus. An accelerometer is coupled to the other end of the shaft. The tip end of the golf club shaft is vibrated and the accelerometer provides a signal indicative of the amplitude and frequency of oscillation of the tip end of the golf club club shaft, which is fed into a computer. The computer is programmed with the stiffness equation for a golf club shaft and is therefore able to compute the stiffness of the shaft based on the frequency of oscillation.